if you stand firmly on a self-lain foundation of patience and trust, someone crossing your boundaries is not so threatening. let them in. see what they do in your space. remove yourself if necessary.
In other words, siblings are forced together, and then suddenly they’re not. The independence of adulthood—when proximity is no longer required and the obligations lessen—creates opportunities for siblings to build, repair, or discard the relationships of their youth, to stay stuck in or break free of the roles they played as children.